They were more readily portable than a longer gun, and were easier for someone to use when on horseback. Since they only needed on hand (and most were one shot) the other hand could handle the reains of a horse, or a sword.
No
One
Handguns were invented as a way to have a small portable gun (as opposed to a rifle) that was easy to keep on your person for defense.
Inexpensive
Self defense, collecting, shooting.
There were single shot pistols and revolvers.
Marlin doesn't manufacture handguns.
No one source of information.
Yes, handguns have a serial number.
That's a very difficult question to answer because, of course, any caliber can kill. Smaller caliber handguns are fairly common in crime involving handguns because people believe large handguns are too diffucult to conceal. Most major police agencies in the U.S. use 9mm or .40 caliber handguns. It's also difficult to answer because information on caliber used in homicide and other crimes isn't readily available.
Yes, handguns were used in WWI, and WWII.
According to http://www.rossiusa.com/company/history.cfm, yes, since 1997.